Sterilization, storage stability and in vivo biocompatibility of poly(trimethylene carbonate)/poly(adipic anhydride) blends

Biodegradable blends of poly(trimethylene carbonate) (PTMC) and poly(adipic anhydride) (PAA) have been proven to be strong candidates for controlled drug delivery polymers in vitro. We now report on the stability, sterilizability and in vivo local tissue response of these matrices. Blend matrices were sterilized by beta-radiation or ethylene oxide gas treatment, stored at different times and temperatures, and analyzed for changes in physicochemical properties. Moisture uptake at different relative humidities and storage times was determined. Sterilization procedures induced hydrolysis of the matrices. Ethylene oxide gas sterilization had a significantly more marked effect upon the matrix properties than radiation treatment. The onset of degradation was reflected in a decrease of crystallinity and molecular weight along with a change of blend composition. A similar onset of matrix degradation was observed upon storage in air. The physicochemical properties of the blends were well preserved upon storage under argon atmosphere. Biocompatibility of PTMC/PAA implants was assessed in the anterior chamber of rabbits eyes for 1 month. At selected post-operative time points, aqueous humor was analyzed for white blood cells and the corneal thickness was measured. The results suggest good biocompatability of PTMC-rich matrices, whereas fast eroding PAA-rich matrices caused inflammatory responses, due to a burst release of degradation products.     

Resorbable elastomeric networks prepared by photocrosslinking of high-molecular-weight poly(trimethylene carbonate) with photoinitiators and poly(trimethylene carbonate) macromers as crosslinking aids

Resorbable and elastomeric poly(trimethylene carbonate) (PTMC) networks were efficiently prepared by photoinitiated crosslinking of linear high-molecular-weight PTMC. To crosslink PTMC films, low-molecular-weight PTMC macromers with methacrylate end groups were synthesized and used as crosslinking aids. By exposing PTMC films containing only photoinitiator (Irgacure(?) 2959) or both photoinitiator and PTMC macromers to ultraviolet light, PTMC networks with high gel contents (87-95%) could be obtained. The crosslink density could be readily varied by adjusting the irradiation time or the amount of crosslinking aid used. The formed networks were flexible, with low elastic modulus values ranging from 7.1 to 7.5MPa, and also showed excellent resistance to creep in cyclic tests. In vitro experiments showed that the photocrosslinked PTMC networks could be eroded by macrophages, and upon incubation in aqueous cholesterol esterase enzyme- or potassium dioxide solutions. The rate of surface erosion of photocrosslinked PTMC networks was significantly lower than that observed for films prepared from linear PTMC. These resorbable PTMC elastomeric networks are compatible with cells and may find application in tissue engineering and controlled release.     

Intraocular degradation behavior of crosslinked and linear poly(trimethylene carbonate) and poly(D,L-lactic acid)

The intraocular degradation behavior of poly(trimethylene carbonate) (PTMC) networks and poly(D,L-lactic acid) (PDLLA) networks and of linear high molecular weight PTMC and PDLLA was evaluated. PTMC is known to degrade by enzymatic surface erosion in vivo, whereas PDLLA degrades by hydrolytic bulk degradation. Rod shaped specimens were implanted in the vitreous of New Zealand white rabbits for 6 or 13 wk. All materials were well tolerated in the rabbit vitreous. The degradation of linear high molecular weight PTMC and PTMC networks was very slow and no significant mass loss was observed within 13 wk. Only some minor signs of macrophage mediated erosion were found. The fact that no significant enzymatic surface erosion occurs can be related to the avascularity of the vitreous and the limited number of cells it contains. PDLLA samples showed more evident signs of degradation. For linear PDLLA significant swelling and a large decrease in molecular weight in time was observed and PDLLA network implants started to lose mass within 13 wk. Of the tested materials, PDLLA networks seem to be most promising for long term degradation controlled intravitreal drug delivery since this material degrades without significant swelling. Furthermore the preparation method of these networks allows easy and efficient incorporation of drugs.     

Synthesis and drug release behavior of poly (trimethylene carbonate)-poly (ethylene glycol)-poly (trimethylene carbonate) nanoparticles

ABA-type triblock copolymers poly (trimethylene carbonate)-poly (ethylene glycol)-poly (trimethylene carbonate) were synthesized by ring-opening polymerization of trimethylene carbonate initiated by dihydroxyl poly (ethylene glycol). The critical micelle concentration of amphiphilic triblock copolymers in aqueous solution was determined by fluorescence spectroscopy using 9-chloromethyl anthracene as fluorescence probe. Core-shell-type nanoparticles were prepared by the dialysis technique. Transmission electron microscopy images showed that these nanoparticles were regularly spherical in shape. Micelle size determined by dynamic light scattering is 50-160 nm. Anticancer drug methotrexate (MTX) as model drug was loaded in the polymeric nanoparticles. X-ray powder diffraction spectra showed that model drugs were molecularly dispersed in the core. In vitro release behavior of MTX was investigated.     

Synthesis and properties of star oligo/poly(trimethylene carbonate)s with cholic acid moieties as cores

Star oligo/poly(trimethylene carbonate)s with cholic acid moieties as cores were synthesized by ring-opening polymerization of trimethylene carbonate (TMC) initiated by cholic acid with hydroxyl groups. The molecular weights of the star oligomers/polymers were controlled by adjusting the feed ratio of the initiator cholic acid to the monomer TMC. The star oligo/poly(trimethylene carbonate)s were characterized by Fourier transform infrared spectroscopy (FT-IR), (1)H nuclear magnetic resonance spectroscopy ((1)H-NMR) and combined size-exclusion chromatography and multiangle laser light scattering (SEC-MALLS) analysis. The water contact angles of the star oligo/poly(trimethylene carbonate)s were measured. Using 3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay, the star oligo/poly(trimethylene carbonate) was proved to have a low cytotoxicity. A microsphere drug-delivery system based on a star polymer was fabricated and its in vitro drug release property was studied.     

Synthesis,characterization and surface modification of low moduli poly(ether carbonate urethane)ureas for soft tissue engineering

Flexible scaffolds are of great interest in engineering functional and mechano-active soft tissues as such scaffolds might allow mechanical stimuli to transfer effectively from the scaffolds to cells during tissue development. Towards this end, we have developed a family of flexible poly(ether carbonate urethane)ureas (PECUUs) with a triblock copolymer poly(trimethylene carbonate)–poly(ethylene oxide)–poly(trimethylene carbonate) (PTMC–PEO–PTMC) or pentablock copolymers PTMC–PEO–PPO–PEO–PTMC (PPO, polypropylene oxide) as soft segments, linked by 1,4-diisocyanatobutane and putrescine. All of the PECUUs had low glass transition temperatures (<?46 °C). The PTMC–PEO–PTMC-containing PECUUs had low tensile strength and breaking strain. Replacing PEO with the similar length PEO–PPO–PEO resulted in highly flexible and soft PECUUs possessing breaking strains of 362–711%, tensile strengths of 8–18 MPa and moduli of 5.5–7.4 MPa at room temperature in air. Under aqueous conditions at 37 °C, these polymers remained flexible while their moduli were decreased to 3.4–4.0 MPa. PECUUs based on PTMC–PEO–PPO–PEO–PTMC were thermosensitive as the water content at 37 °C was lower than that at 4 °C. PECUU using PTMC–PEO–PTMC as a soft segment showed 30% weight loss over 6 weeks in PBS at 37 °C, while that using PTMC–PEO–PPO–PEO–PTMC as a soft segment had weight loss <6%. Degradation products were found to lack cytotoxicity. The mechanical stresses and moduli of PECUUs based on PTMC–PEO–PPO–PEO–PTMC were unchanged during the degradation. To enhance cell adhesion, PECUUs were surface modified with Arg-Gly-Asp-Ser (RGDS). Smooth muscle cell adhesion was 114% of tissue culture polystyrene for unmodified PECUU and >180% for RGDS-modified PECUUs, with cell viability on both surfaces increasing during culture. These low moduli polyurethanes may find applications in engineering cardiovascular or other soft tissues.     

Macrophage-mediated erosion of gamma irradiated poly(trimethylene carbonate) films

A macrophage culture model was used to investigate the erosion of gamma irradiated poly(trimethylene carbonate) (PTMC) films. When the PTMC films were incubated in the culture medium, but physically separated from the cells by a membrane, no erosion occurred. In contrast, when the J774A macrophages were directly cultured on PTMC films, they adhered to the films and were found to have eroded the polymer surface. Macrophages adhered to gamma irradiated poly(?-caprolactone) (PCL) controls as well, but to a lesser extent than to the PTMC films. In this case, no signs of erosion were observed. Human skin fibroblasts cultured on PTMC and PCL films as controls also adhered to the films but did not erode the surfaces. The effect of enzymes and reactive oxygen species that can be secreted by macrophages on the erosion process was assessed using aqueous solutions of cholesterol esterase, lipoprotein lipase, esterase, potassium superoxide, and hydrogen peroxide. The PTMC films eroded in aqueous enzyme solutions as well as in aqueous superoxide solutions. Cholesterol esterase and superoxide anion radicals seem to be most involved in the macrophage-mediated erosion of PTMC. This macrophage culture model is useful in assessing the influence of macrophages on the in vivo biodegradability of polymers and in elucidating the biodegradation mechanisms involved.     

The in vivo and in vitro degradation behavior of poly(trimethylene carbonate)

The in vivo and in vitro degradation behavior of poly(trimethylene carbonate) (PTMC) polymers with number average molecular weights of 69 x 10(3), 89 x 10(3), 291 x 10(3) and 457 x 10(3)g/mol (respectively abbreviated as PTMC(69), PTMC(89), PTMC(291) and PTMC(457)) was investigated in detail. PTMC rods (3mm in diameter and 4mm in length) implanted in the femur and tibia of rabbits degraded by surface erosion. The mass loss of high molecular weight PTMC(457) specimens was 60wt% in 8 wks, whereas the mass loss of the lower molecular weight PTMC(89) specimens in the same period was 3 times lower. PTMC discs of different molecular weights immersed in lipase solutions (lipase from Thermomyces lanuginosus) degraded by surface erosion as well. The mass and thickness of high molecular weight PTMC(291) discs decreased linearly in time with an erosion rate of 6.7 microm/d. The erosion rate of the lower molecular weight PTMC(69) specimens was only 1.4mum/d. It is suggested that the more hydrophilic surface of the PTMC(69) specimens prevents the enzyme from acquiring a (hyper)active conformation. When PTMC discs were immersed in media varying in pH from 1 to 13, the non-enzymatic hydrolysis was extremely slow for both the high and low molecular weight samples. It can be concluded that enzymatic degradation plays an important role in the surface erosion of PTMC in vivo.     

Creep-resistant elastomeric networks prepared by photocrosslinking fumaric acid monoethyl ester-functionalized poly(trimethylene carbonate) oligomers

Biodegradable elastomeric networks were prepared from ethyl fumarate-functionalized poly(trimethylene carbonate) oligomers. Photocrosslinkable macromers were synthesized by reacting three-armed, hydroxyl group-terminated poly(trimethylene carbonate) oligomers with fumaric acid monoethyl ester at room temperature using N,N-dicyclohexylcarbodiimide as a coupling agent and 4-dimethylamino pyridine as a catalyst. Poly(trimethylene carbonate) macromers with molecular weights ranging between 4500 and 13,900 were prepared and crosslinked by ultraviolet-initiated radical polymerization. The gel contents of the resulting transparent networks varied between 74% and 80%. All obtained networks had low glass transition temperatures, which varied between ?18 and ?13 °C. They showed rubber-like behavior and excellent mechanical properties, with tensile strengths and elongations at break of up to 17.5 MPa and 750%, respectively. Moreover, static- and dynamic creep experiments showed that these amorphous networks were highly elastic and resistant to creep. In cyclic tensile testing to 50% strain, the permanent deformation after 20 cycles was 0%, while static creep tests at 35% of the yield stress did not indicate creep or permanent deformation after removal of the load. Porous structures were prepared by photopolymerizing the macromers in the presence of salt particles, and subsequent leaching of the salt. Such networks, built up of non-toxic compounds and designed to release benign degradation products, may find application as tissue engineering scaffolds for dynamic cell culture.     

Introduction of enzymatically degradable poly(trimethylene carbonate) microspheres into an injectable calcium phosphate cement

Poly(trimethylene carbonate) (PTMC) is an enzymatically degradable polyester with rubber-like properties. Introduction of this polymer into an injectable calcium phosphate bone cement can therefore be used to introduce macroporosity into the cement for tissue engineering purposes as well as to improve mechanical properties. Aim of this study was to investigate calcium phosphate cements with incorporated PTMC microspheres (PTMC CPCs) on their physical/mechanical properties and in vitro degradation characteristics. Therefore, composites were tested on setting time and mechanical strength as well as subjected to phosphate buffered saline (PBS) and enzyme containing medium. PTMC CPCs (12.5 and 25 wt%) with molecular weights of 52.7 kg mol(-1) and 176.2 kg mol(-1) were prepared, which showed initial setting times similar to that of original CPC. Though compression strength decreased upon incorporation of PTMC microspheres, elastic properties were improved as strain-at-yield increased with increasing content of microspheres. Sustained degradation of the microspheres inside PTMC CPC occurred when incubated in the enzymatic environment, but not in PBS, which resulted in an interconnected macroporosity for the 25 wt% composites.     

Guided bone regeneration in rat mandibular defects using resorbable poly(trimethylene carbonate) barrier membranes

The present study evaluates a new synthetic degradable barrier membrane based on poly(trimethylene carbonate) (PTMC) for use in guided bone regeneration. A collagen membrane and an expanded polytetrafluoroethylene (e-PTFE) membrane served as reference materials. In 192 male Sprague-Dawley rats, a standardized 5.0mm circular defect was created in the left mandibular angle. New bone formation was demonstrated by post mortem micro-radiography, micro-computed tomography imaging and histological analysis. Four groups (control, PTMC, collagen, e-PTFE) were evaluated at three time intervals (2, 4 and 12 weeks). In the membrane groups the defects were covered; in the control group the defects were left uncovered. Data were analysed using a multiple regression model. In contrast to uncovered mandibular defects, substantial bone healing was observed in defects covered with a barrier membrane. In the latter case, the formation of bone was progressive over 12 weeks. No statistically significant differences between the amount of new bone formed under the PTMC membranes and the amount of bone formed under the collagen and e-PTFE membranes were observed. Therefore, it can be concluded that PTMC membranes are well suited for use in guided bone regeneration.     

Evaluation of tubular poly(trimethylene carbonate) tissue engineering scaffolds in a circulating pulsatile flow system

Tubular scaffolds (internal diameter approximately 3 mm and wall thickness approximately 0.8 mm) with a porosity of approximately 83% and an average pore size of 116 μm were prepared from flexible poly(trimethylene carbonate) (PTMC) polymer by dip-coating and particulate leaching methods. PTMC is a flexible and biocompatible polymer that crosslinks upon irradiation; porous network structures were obtained by irradiating the specimens in vacuum at 25 kGy before leaching soluble salt particles. To assess the suitability of these scaffolds in dynamic cell culturing for cardiovascular tissue engineering, the scaffolds were coated with a thin (0.1 to 0.2 mm) non-porous PTMC layer and its performance was evaluated in a closed pulsatile flow system (PFS). For this, the PFS was operated at physiological conditions at liquid flows of 1.56 ml/s with pressures varying from 80-120 mmHg at a frequency of 70 pulsations per minute. The mechanical properties of these coated porous PTMC scaffolds were not significantly different than non-coated scaffolds. Typical tensile strengths in the radial direction were 0.15 MPa, initial stiffness values were close to 1.4 MPa. Their creep resistance in cyclic deformation experiments was excellent. In the pulsatile flow setup, the distention rates of these flexible and elastic scaffolds were approximately 0.10% per mmHg, which is comparable to that of a porcine carotid artery (0.11% per mmHg). The compliance and stiffness index values were close to those of natural arteries.?In long-term deformation studies, where the scaffolds were subjected to physiological pulsatile pressures for one week, the morphology and mechanical properties of the PTMC scaffolds did not change. This suggests their suitability for application in a dynamic cell culture bioreactor.     

Synthesis, characterization and in vitro degradation of a new family of alternate poly(ester-anhydrides) based on aliphatic and aromatic diacids

A new family of alternate poly(ester-anhydrides) containing aliphatic and aromatic diacids were synthesized. The dicarboxylic acids were obtained by derivatization of p-hydroxy benzoic acid at the hydroxy terminus with cyclic anhydride (adipic anhydride and succinic anhydride) and subsequently polymerized via the corresponding mixed anhydrides by melt polycondensation. DSC traces revealed that the polymers had low Tg (< 40 degrees C) and no crystallinity. The static contact angle measurements indicated that the poly(ester-anhydrides) were more hydrophobic than poly(D,L-lactide) and poly(adipic anhydride). In vitro degradation of the polymers was also investigated in pH 7.4 PBS at 37 degrees C. It was found that degradation rate of the poly(ester-anhydrides) increased with p-carboxy phenyl adipic monoester (CPA) content in the polymers and the degradation duration could be adjusted from ca. 20 days to ca. 2 months. Erosion curve of poly(p-carboxy phenyl adipic monoester anhydride) (PCPA) was characterized by a linear region of weight loss at nearly constant rate in the first 7 days (ca. 80% of weight loss) followed by a gradual decrease region. IR and SEM analysis showed that significant erosion of PCPA occurred in the outer layer and no apparent erosion could be seen in the inner layer of the degrading sample after 7-day degradation. The poly(ester-anhydrides) may be used as either anti-infective polymeric prodrugs or matrices for drug delivery.     

The fate of ultrafast degrading polymeric implants in the brain

We have recently reported on an ultrafast degrading tyrosine-derived terpolymer that degrades and resorbs within hours, and is suitable for use in cortical neural prosthetic applications. Here we further characterize this polymer, and describe a new tyrosine-derived fast degrading terpolymer in which the poly(ethylene glycol) (PEG) is replaced by poly(trimethylene carbonate) (PTMC). This PTMC containing terpolymer showed similar degradation characteristics but its resorption was negligible in the same period. Thus, changes in the polymer chemistry allowed for the development of two ultrafast degrading polymers with distinct difference in resorption properties. The in vivo tissue response to both polymers used as intraparenchymal cortical devices was compared to poly(lactic-co-glycolic acid) (PLGA). Slow resorbing, indwelling implant resulted in continuous glial activation and loss of neural tissue. In contrast, the fast degrading tyrosine-derived terpolymer that is also fast resorbing, significantly reduced both the glial response in the implantation site and the neuronal exclusion zone. Such polymers allow for brain tissue recovery, thus render them suitable for neural interfacing applications.     

Flexible, elastic and tear-resistant networks prepared by photo-crosslinking poly(trimethylene carbonate) macromers

Poly(trimethylene carbonate) (PTMC) macromers with molecular weights (M(n)) between 1000 and 41,000gmol(-1) were prepared by ring opening polymerization and subsequent functionalization with methacrylate end groups. Flexible networks were obtained by radical photo-crosslinking reactions of these macromers. With increasing molecular weight of the macromer the networks obtained showed increasing swelling ratios in chloroform and decreasing glass transition temperatures, reaching a constant value of approximately -18°C, which is close to that of linear high molecular weight PTMC. For all prepared networks the creep resistance was high. However, the molecular weight of the macromer strongly influenced the tensile properties of the networks. With increasing molecular weight of the macromer the E-modulus of the networks decreased from 314MPa (lowest M(n)) to 5MPa (highest M(n)), while their elongation at break continuously increased, reaching a very high value of 1200%. The maximum tensile strength values of the networks were found to first decrease with increasing M(n), but to increase again at values above approximately 10,000gmol(-1), at which the networks started to show rubber-like behavior. The toughness (area under the stress-strain curves, W) determined in tensile testing experiments, in tear propagation experiments, and in suture retention strength measurements showed that PTMC networks prepared from the higher molecular weight macromers (M(n)>10,000gmol(-1)) were tenacious materials. The mechanical properties of these networks compare favorably with those of linear high molecular weight PTMC and well-known elastomeric materials like silicone rubber (poly(dimethylsiloxane)) and natural latex rubber. Additionally they also compare well with those of native blood vessels, which may be of importance in the use of these materials for the tissue engineering of small diameter blood vessels.     

A surface-eroding antibiotic delivery system based on poly-(trimethylene carbonate)

Biodegradable delivery systems that do not produce acidic compounds during degradation are preferred for local antibiotic delivery in bone infections in order to avoid adverse bone reactions. Poly(trimethylene carbonate) (PTMC) has good biocompatibility, and is such a polymer. The objective of this in vitro study was to explore the suitability of PTMC as an antibiotic releasing polymer for the local treatment of bone infections. Degradation behaviour and corresponding release profiles of gentamicin and vancomycin from slowly degrading PTMC₁₆₈ and faster degrading PTMC₃₃₉ discs were compared in the absence and presence of a lipase solution. Gentamicin release in the absence of lipase was diffusion-controlled, while vancomycin release was limited. Surface erosion of PTMC only occurred in the presence of lipase. Both antibiotics were released in high concentrations from PTMC in the presence of lipase through a combination of surface erosion and diffusion. This illustrates the major advantage of surface-eroding biodegradable polymers, allowing release of larger antibiotic molecules like vancomycin.     

Designing porosity and topography of poly(1,3-trimethylene carbonate) scaffolds

Using phase separation micromolding (PSμM) we developed porous micro-patterned sheets from amorphous poly(1,3-trimethylene carbonate) (PTMC). The use of these PTMC sheets can be advantageous in tissue engineering applications requiring highly flexible constructs. Addition of poly(ethylene oxide) (PEO) in various amounts to PTMC casting solutions provides PTMC sheets with tailored porosity and pore sizes in the range 2–20 μm. The pore-forming effect of PEO during the phase separation process is evaluated and glucose transport measurements show that the pores are highly interconnected. Additionally, tailoring the micro-pattern design yields PTMC sheets with various surface topographies. Cell culturing experiments with C2C12 pre-myoblasts revealed that cell attachment and proliferation on these sheets is relatively high and that the micro-pattern topography induces a clearly defined cell organization.     

A New Insight Into the Mechanism of the Ring‐Opening Polymerization of Trimethylene Carbonate Catalyzed by Methanesulfonic Acid

The ring‐opening polymerization (ROP) of trimethylene carbonate (TMC) initiated by a monoalcohol and catalyzed by CH₃SO₃H is investigated, in an effort to reveal extra features of the known activated monomer/active chain‐end (AM/ACE) combined mechanism. Size‐exclusion chromatography (SEC) profiles obtained with high‐molar‐mass samples show a poly(trimethylene carbonate) (PTMC) fraction generated by AM/ACE with a molar mass that is exactly twice that of the PTMC fraction coming from pure AM. Conversely, PTMC prepared with a diol is perfectly unimodal and keeps its molar mass dispersity below 1.1. This suggests that the side AM/ACE mechanism may be a bidirectional AM mechanism, and that PTMC with a narrow unimodal molar‐mass distribution can be obtained easily from a diol regardless of this side propagation.     

Development of Ester Free Type Poly(trimethylene carbonate) Derivatives with Pendant Fluoroaromatic Groups

The facile method for the synthesis of ester free type poly(trimethylene carbonate) (PTMC) derivatives is previously reported. In this paper, a series of PTMC derivatives with fluoroaromatic groups in the side chain are synthesized to improve polymer properties. Thermal analysis reveals that all the PTMC derivatives have a decomposition temperature exceeding 300 °C. Furthermore, as the number of fluorine attached to the aromatic ring increases, the glass transition temperature decreases. In order to clarify the surface properties of their films, the contact angles and protein adsorption are evaluated. The hydrophobic nature is attributed to the fluorine groups at the side chain. Furthermore, it is suggested that as the number of fluorine attached to the aromatic ring increases, the protein adsorption is suspended. There is a possibility that a new biomaterial could be created by introducing a fluoroaromatic group into the side chain of PTMC with ester free structure.     

Synthesis of Poly(trimethylene carbonate) Oligomers by Ring‐Opening Polymerization in Bulk

Telechelic poly(trimethylene carbonate) (PTMC) oligomers are synthesized and carefully characterized with molar masses between 300 and 5000 g mol^?1 in bulk by ring‐opening polymerization (ROP) with 1,3‐dioxan‐2‐one (trimethylene carbonate or TMC) as monomer and 1,4‐butanediol (BDO) as co‐initiator. 1,5,7‐Triazabicyclo[4.4.0]dec‐5‐ene (TBD) organic catalyst and tin(II) bis(2‐ethylhexanoate) (Sn(Oct)₂) organometallic initiator are chosen comparatively. Due to the bi‐functionality of BDO and relatively low TMC/BDO feed ratios, it is proved that PTMC chains are elaborated from one or both the BDO alcohol functions, producing two coexisting kinds of PTMC chains with BDO unit at the chain end or in the backbone. Additionally, PTMC chains bear permanent and fast exchange reactions at 100 °C, leading to both a dynamic redistribution of chains and their extension with BDO unit numbers mainly from 0‐4 but up to 6. Longer reaction times and lower TMC/BDO molar ratios bring about more predominant exchange reactions and MALDI‐TOF allows to detail the structures evolutions deeply. Better average molar masses control and narrower distributions are obtained with TBD as compared to Sn(Oct)₂. PTMC molar masses can be predicted simply by the TMC/BDO feed ratio with TBD. Kinetically, TBD is the most efficient. The glass transition temperature T_g is found to respect Flory–Fox model.