Random poly(ε‐caprolactone‐L‐alanine) by direct melt copolymerization

A series of random polyesteramides (PEAs) with a range of molar composition from 90/10 to 50/50 were synthesized by direct melt polycondensation of ε‐caprolactone and l ‐alanine. Their structure was fully characterized by Fourier transform IR and NMR spectroscopy. The resulting copolymers are completely amorphous with the exception of PEA‐90/10 which possesses a semicrystalline structure. These PEAs present increasing glass transition temperatures at increasing l ‐alanine contents and exhibit fairly good thermal stability with 10% mass loss temperatures reaching 315 °C. © 2020 Society of Industrial Chemistry     

Physical and thermal properties of l‐lactide/ϵ‐caprolactone copolymers: the role of microstructural design

Understanding the underlying role of microstructural design in polymers allows for the manipulation and control of properties for a wide range of specific applications. As such, this work focuses on the study of microstructure–property relationships in l‐ lactide/?‐caprolactone (LL/CL) copolymers. One‐step and two‐step bulk ring‐opening polymerization (ROP) procedures were employed to synthesize LL/CL copolymers of various compositions and chain microstructures. In the one‐step procedure, LL and CL were simultaneously copolymerized to yield P(LL‐<i>stat</i>‐CL) statistical copolymers. In the two‐step procedure, poly(l‐ lactide) (PLL) and poly(?‐caprolactone) (PCL) prepolymers were synthesized in the first step before CL and LL respectively were added in the second step to yield P[LL‐<i>b</i>‐(CL‐<i>stat</i>‐LL)‐<i>b</i>‐LL] and P[CL‐<i>b</i>‐(LL‐<i>stat</i>‐CL)‐<i>b</i>‐CL] block copolymers as the final products. The findings reveal that, in addition to the copolymerization procedure employed, the length and type of the prepolymer play important roles in determining the chain microstructure and thereby the overall properties of the final copolymer. Moreover, control over the degree of crystallinity and the type of crystalline domains, which is controlled during the polymer chemistry process, heavily influences the physical and mechanical properties of the final polymer. In summary, this work describes an interesting approach to the microstructural design of biodegradable copolymers of LL and CL for potential use in biomedical applications. © 2019 Society of Chemical Industry     

On globally stable adaptive control providing l 1 tracking performance for linear discrete-time systems

Existing adaptive control algorithms at best guarantee that the tracking error is a <i>l</i> <sub>2</sub> sequence. This paper presents globally stable adaptive control algorithms for linear discrete-time systems providing <i>l</i> <sub>1</sub> tracking performance. Two algorithms with different degree of complexity are proposed, one for the case of known control directions, and a separate algorithm for the case of unknown control directions. It is demonstrated that in both cases the tracking error is <i>l</i> <sub>1</sub> sequence, while the input and output signals are uniformly bounded.     

Effect of the composition and degree of crosslinking on the properties of poly(l‐lactic acid)/crosslinked polyurethane blends

Poly(l ‐lactic acid)/crosslinked polyurethane (PLLA/CPU) blends which were prepared via reactive blending of PLLA with poly(<i>?</i>‐caprolactone) (PCL), glycerol and 4,4′‐methylenediphenyl diisocyanate showed excellent toughness. The effects of the composition of the mixture and degree of crosslinking of CPU on the toughness of the PLLA/CPU blends (80/20 w/w) were studied in detail. Dynamic mechanical analysis and rheological measurements were used to characterize the structure of the <i>in situ</i> formed CPU in the PLLA matrix. A novel netlike phase structure was observed when the average molecular weight of PCL and degree of crosslinking were 1 kDa and 10%, respectively. The impact strength of the blend was enhanced from 2.2 kJ m<sup>?2</sup> for pure PLLA to 62.4 kJ m<sup>?2</sup>; meanwhile, the elongation at break was increased to 489.8%. Therefore, the mechanical properties of PLLA/CPU blends can be easily tailored by tuning the composition of the mixture and the degree of crosslinking of CPU. © 2018 Society of Chemical Industry     

我国有色金属行业走势和及未来发展对策

我国是一个有色金属资源匮乏的国家,对国外的有色金属资源需求量很大,文中分析了我国有色金属行业的现状及存在问题,提出了我国有色金属产业整合、海外发展和注重环境的发展方向。     

福建紫金矿业股份有限公司硫化铜矿生物堆浸过程

针对紫金山铜矿的特点 ,进行生物堆浸提铜工业试验研究。结果表明 ,紫金山铜矿生物堆浸效果良好 ,不同浸矿堆累计浸出时间 10 0 0h ,浸出率在 40 %～ 60 % ,浸出半年 ,浸出率达 80 %以上。次生硫化铜矿物的生物堆浸具有两个阶段 ,在浸出前一阶段 ,浸出速率较快 ,而浸出第二阶段浸出速率较慢。随着浸出的进行 ,浸出液 pH连续下降 ,溶液电位逐步升高。微生物的存在加速堆中Fe2 氧化使溶液电位上升 ,同时氧化中间过程的产物元素硫 ,从而加速硫化矿的氧化溶解。     

六角晶系铁氧体轴比及晶粒均匀性的控制

介绍了一种六角晶系铁氧体轴比及晶粒均匀性的控制方法，并对烧结磁体取向度的提高作了讨论。指出等径预处理为今后研制高能积永磁铁氧体找到了新途径。     

商业用地路线价测算模型研究

商业用地地价受区位影响较大 ,在进行商业用地基准地价评估时 ,单纯采用级别基准地价不能完全反映不同区位土地的地价差异。为准确地反映临街商业用地的地价水平 ,应建立商业用地路线价。本文以博兴县为例 ,利用商业出租样点资料建立了路线价测算模型 ,实际应用效果良好     

高层或多层建筑中错层的一种结构构造处理

从高层建筑中结构错层导致薄弱环节的机理出发,找出了症结所在。提出了区分建筑错层与结构错层概念的观点、实现建筑有错层而结构无错层的思想以及通过构造措施消除薄弱环节的设计方法