This week, the overall grades of four chemicals stocks are lower, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

PolyOne Corporation’s (POL) rating falls to a D (“sell”) this week, down from C (“hold”) the week prior. PolyOne is an international polymer services company with operations in North America, Europe, Asia, Australia, and South America. In Portfolio Grader’s specific subcategories of Earnings Growth, Earnings Momentum and Sales Growth, POL also gets an F. The stock has a trailing PE Ratio of 26.00. To get an in-depth look at POL, get Portfolio Grader’s complete analysis of POL stock.

Marrone Bio Innovations, Inc. (MBII) earns an F (“strong sell”) this week, moving down from last week’s grade of D (“sell”). The stock receives F’s in Earnings Momentum, Equity, Cash Flow and Sales Growth. Trade volume is up 405.9% from the previous week. For more information, get Portfolio Grader’s complete analysis of MBII stock.

Kraton Performance Polymers, Inc. (KRA) gets weaker ratings this week as last week’s D drops to an F. Kraton Performance Polymers produces engineered polymers and styrenic block copolymers. The stock gets F’s in Earnings Momentum and Earnings Surprise. To get an in-depth look at KRA, get Portfolio Grader’s complete analysis of KRA stock.

Huntsman Corporation (HUN) experiences a ratings drop this week, going from last week’s C to a D. Huntsman manufactures differentiated and commodity chemical products. The stock gets F’s in Earnings Momentum, Earnings Revisions and Earnings Surprise. For more information, get Portfolio Grader’s complete analysis of HUN stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.