Vinyl-Addition Homopolymeization of Norbornenes with Bromoalkyl Groups.

Vinyl-addition polynorbornenes are of great interest as versatile templates for the targeted design of polymer materials with desired properties. These polymers possess rigid and saturated backbones, which provide them with high thermal and chemical stability as well as high glass transition temperatures. Vinyl-addition polymers from norbornenes with bromoalkyl groups are widely used as precursors of anion exchange membranes; however, high-molecular-weight homopolymers from such monomers are often difficult to prepare. Herein, we report the systematic study of vinyl-addition polymerization of norbornenes with various bromoalkyl groups on Pd-catalysts bearing N-heterocyclic carbene ligands ((NHC)Pd-systems). Norbornenes with different lengths of hydrocarbon linker (one, two, and four CH2 groups) between the bicyclic norbornene moiety and the bromine atom were used as model monomers, while single- and three-component (NHC)Pd-systems were applied as catalysts. In vinyl-addition polymerization, the reactivity of the investigated monomers varied substantially. The relative reactivity of these monomers was assessed in copolymerization experiments, which showed that the closer the bromine is to the norbornene double-bond, the lower the monomer's reactivity. The most reactive monomer was the norbornene derivative with the largest substituent (with the longest linker). Tuning the catalyst's nature and the conditions of polymerization, we succeeded in synthesizing high-molecular-weight homopolymers from norbornenes with bromoalkyl groups (Mn up to 1.4 × 106). The basic physico-chemical properties of the prepared polymers were studied and considered together with the results of vinyl-addition polymerization.

Novel Poly(Methylenelactide-g-L-Lactide) Graft Copolymers Synthesized by a Combination of Vinyl Addition and Ring-Opening Polymerizations.

In this work, a novel poly (methylenelactide-g-L-lactide), P(MLA-g-LLA) graft copolymer was synthesized from poly(methylenelactide) (PMLA) and L-lactide (LLA) using 0.03 mol% liquid tin(II) n-butoxide (Sn(OnBu)2) as an initiator by a combination of vinyl addition and ring-opening polymerization (ROP) at 120 °C for 72 h. Proton and carbon-13 nuclear magnetic resonance spectroscopy (1H- and 13C-NMR) and Fourier-transform infrared spectroscopy (FT-IR) confirmed the grafted structure of P(MLA-g-LLA). The P(MLA-g-LLA) melting temperatures (Tm) range of 144-164 °C, which was lower than that of PLA (170-180 °C), while the thermal decomposition temperature (Td) of around 314-335 °C was higher than that of PLA (approx. 300 °C). These results indicated that the grafting reaction could widen the melt processing range of PLA and in doing so increase PLA's thermal stability during melt processing. The graft copolymers were obtained with weight-average molecular weights (M¯w) = 4200-11,000 g mol-1 and a narrow dispersity (D = 1.1-1.4).