SynopsisEffective chain extenders for linear polyesters were investigated among some bis-heterocycles, which were capable of coupling carboxyl terminals of the polyesters through addition reaction. Consequently, 2,2-bis(2-oxazoline), 2,2-bis(5,6-dihydro-4H-1,3-oxazine) and N,N-hexamethylenebis(carbamoyl-2oxazoline) were found to be the most effective chain extenders. Starting from a poly(ethy1ene terephthalate) (PET) having intrinsic viscosity ([q]) of 0.66 and carboxyl content (CV) of 46 eq/106 g, one could obtain polyesters with [q] of above 1.0 and CV of below 5 eq/106 g in the presence of the chain extenders. Typical reaction condition for the coupling of PET was heating PET under atmospheric nitrogen above its melting temperature with 0.5 mol % of a chain extenders only for several minutes. Bis-2-thiazolines showed no effect under the condition investigated, while in case of bis-2-imidazolines definite degradation was observed. Bis-N-acylaziridines and bisiminocarbonates resulted in some gel1 formation, indicative of side reactions.

Since calcium carbonate is one of the most abundant biogenic minerals found in nature, it is no surprise that there has been a huge focus on its formation and use. In this review, we intend to cover the use of amorphous calcium carbonate, which is the most unstable polymorph of calcium carbonate, for the design of new materials. Amorphous calcium carbonate has been used to manipulate the morphology of new materials, and to create strong inorganic/organic hybrid materials based on biological examples. The exoskeletons of crustaceans, sea shell nacre, and brittle star eyes are a few of the examples discussed here, and researchers have looked at these biominerals for the design of new materials. By using polymer additives and organic synthetic layers to substitute for the natural proteins used in biological systems, interesting hybrid materials have been developed. By taking inspiration from this research, new ideas for the design of the fusion materials can be achieved.

Chitin/CaCO3 hybrids with helical structures are formed through a biomineralization-inspired crystallization process under ambient conditions. Liquid-crystalline chitin whiskers are used as helically ordered templates. The liquid-crystalline structures are stabilized by acidic polymer networks which interact with the chitin templates. The crystallization of CaCO3 is conducted by soaking the templates in the colloidal suspension of amorphous CaCO3 (ACC) at room temperature. At the initial stage of crystallization, ACC particles are introduced inside the templates, and they crystallize to CaCO3 nanocrystals. The acidic polymer networks induce CaCO3 crystallization. The characterization of the resultant hybrids reveals that they possess helical order and homogeneous hybrid structures of chitin and CaCO3 , which resemble the structure and composition of the exoskeleton of crustaceans.

SynopsisThe reaction behavior of such bis cyclic-imino-ethers as 2, 2'-bis(2-oxazoline), which had been proved in the previous paper to be an effective chain extender to couple carboxyl terminals of linear polyesters through addition reaction, has been studied to evaluate their practical applicability as the chain extenders for poly(ethy1ene terephthalate) and poly(buty1ene terephthalate). It has been observed that a wide range of excess use of 2,2'-bis(2-oxazoline) resulted in polyesters of almost similar molecular weight. In addition, when excess amounts of the chain extender were added and the reaction conditions were fixed, the ratio of the coupled carboxyl terminals to the initial carboxyl terminals became constant regardless of the initial molecular weight and carboxyl content (CV). The results indicate that the chain-extended polyesters possess predetermined molecular weight and CV, both of which depend only on the molecular weight and CV of the initial polymers, and not on the amount of the chain extender added. INTRODUCTIONPoly(ethy1ene terephthalate) (PET) and poly(buty1ene terephthalate) (PBT) are well known as commercially important polymeric materials. Many studies have been carried out to improve their performances. Among such studies, a technology to manufacture the polymers of very high molecular weight and low carboxyl content has been regarded as very significant to improve their mechanical and chemical properties such as tenacity and hydrolytic stability. The use of so-called "chain extenders" seems attractive for that purpose. The chain extenders here mean bifunctional compounds which can react with the polymer end groups very readily, when they are added to the polymer melts, resulting in the higher-molecular-weight polymers easily.For the last several years, we have been making efforts to find more effective chain extenders, especially "addition-type chain extenders," which are reactive with the polymer terminal groups through addition reactions without generating any byproducts.Our previous paper reported that bis cyclic-imino-ether compounds had been proved to be effective carboxyl-addition type chain extenders.l Especially, those having highly electron-withdrawing substituents at the 2-POsition of the cyclic-imino-ethers, such as 2,2'-bis(2-oxazoline), 2,2'-bis(5,6-dihydro-4H-l,3-oxazine), and N,N'-hexamethylenebis (2-carbamoyl-2-oxazoline) were so highly effective as to result in PET having intrinsic viscosity ([TI) above 1.0 and carboxyl content (CV) below 5 eq/106g starting from

SynopsisEffective chain extenders for linear polyesters such as poly(ethy1ene terephthalate) (PET) and poly(buty1ene terephthalate) (PBT) were sought among some nitrogen-containing bisheterocycles, which were reactive with hydroxyl terminals of the polyesters to form addition linkages. Tested were such bis cyclic-imino-esters as bis[5(4H)-oxazolonels (Om) and bis(4H-3,l-benzoxazin-4-one)s (BNZ), among which BNZ, especially 2,2'-bis(4H-3,l-benzoxazin-l-one) (BNZ-A-1) has been proved to be a very effective chain extender for both PET and PBT. Starting from PET having intrinsic viscosity ([q]) of 0.52 and carboxyl content (CV) of 10 eq/106 g, addition of 1 mol % BNZ-A-1 resulted in PET having [ql of 1.11 and CV of 13 eq/106 g a t a polyester melt temperature under atmospheric nitrogen within a few minutes. On the other hand, OXZ which were less thermally stable than BNZ could not act as good chain extenders for PET at a PET melt temperature. But they were effective in the case of PBT, which melted a t a lower temperature than PET.